First, a conventional special effect apparatus will be described with reference to FIG. 1.
So far, in a field of image processing apparatuses, a special effect apparatus for performing 3-D image transformation for a source video signal supplied from an external apparatus has been realized. In this type of the special effect apparatus, a shadow is attached to an object video signal which has been image-transformed to 3-D position to generate stereoscopic effect. The object video signal is a video signal to be 3-D transformed. In the conventional special effect apparatus, in order to attach a shadow to the object video signal, an operator operates a pointing device such as a 3-D joystick to perform a desired first 3-D transformation processing for a first source video signal which is the basis of the object video signal. As shown in FIG. 1A, the 3-D transformed video signal is represented as an object video signal Vobj, and the object video signal Vobj is displayed on a monitor. Next, the operator operates the pointing device to perform a second 3-D transformation processing for a second source video signal, which is the basis of a shadow video signal, for example, of which color is black. Specifically, the operator performs the 3-D transformation processing for a video signal having the color of shadow so that the 3-D transformed shadow video signal Vshadow looks like the shadow of the object video signal Vobj displayed on the monitor.
However, in such conventional special effect apparatus, since the 3-D transformation processing is respectively performed for the object video signal Vobj and the shadow video signal Vshadow, it is very difficult to produce the shadow video signal Vshadow which looks like a natural shadow as the shadow of the object video signal Vobj. In addition, even the skilled operator repeats trial-and-error to produce the shadow video signal Vshadow which looks like the natural shadow, so that there has been a problem that it takes a long time to produce the shadow video signal.
Further, in such conventional special effect apparatus, as aforementioned above, since the 3-D transformation processing is respectively performed for the object video signal Vobj and the shadow video signal Vshadow, even if the object video signal Vobj shown in FIG. 1A is 3-D transformed to a position of an object video signal Vobj' shown in FIG. 1B, the shadow video signal Vshadow does not move. Therefore, a new natural shadow has to be produced for the object video signal Vobj'. Accordingly, since the shadow video signal has to be produced whenever the object video signal is 3-D transformed, there has been a problem that the operation is very complicated.